This invention relates to novel piperidine derivatives of formula (I) and a process for the preparation thereof. 
wherein
R1 is H or C1-C6alkyl wherein the C1C6alkyl moiety is straight or branched;
R2 is xe2x80x94COOH or xe2x80x94COOalkyl wherein the alkyl moiety has from 1 to 6 carbon atoms and is straight or branched; or
stereoisomers or pharmaceutically acceptable acid addition salt thereof.
Terfenadine, xcex1-[4-(1,1-dimethylethyl)phenyl]-4-(hydroxydiphenylmethyl)-1-piperidinebutanol, is a known antihistaminic agent which is currently available commercially under the name Seldane(copyright) with a recommended dosage of 60 mg b.i.d. (See PHYSICIAN""S DESK REFERENCE, 52nd Edition, 1998, pp.1238-1244, Medical Economics Data, a division of Medical Economics Company, Inc. Montvale, N.J.). Terfenadine is disclosed in U.S. Pat. No. 3,878,217, issued Apr. 15, 1975. Sorken and Heel have provided a review of the pharmacodynamic properties and therapeutic efficacy of terfenadine [Drugs 29, 34-56 (1985)].
Terfenadine undergoes extensive (99%) first pass metabolism to two primary metabolites (fexofenadine) and an inactive dealkylated metabolite. Fexofenadine, a.k.a. 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl-xcex1,xcex1-dimethyl-benzeneacetic acid, has been disclosed as an antihistaminic agent having oral activity in U.S. Pat. No.4,254,129, issued Mar. 3, 1981. It is currently available commercially under the name Allegra(copyright) (See PHYSICIAN""S DESK REFERENCE, 52nd Edition, 1998, pp.1189-1190, Medical Economics Data, a division of Medical Economics Company, Inc. Montvale, N.J.).
An object of the present invention is to provide novel piperidine derivatives of formula (I) useful for the treatment of allergic disorders. It is a further object to provide a process for the preparation of said derivatives and to provide novel intermediates useful for preparation of the same.
Additionally, it is an object of the present invention to provide a method of treating a patient suffering from an allergic disorder comprising administering to said 10 patient an effective antiallergic amount of a compound of formula (I).
Furthermore, it is an object of the present invention to provide a composition comprising an assayable amount of a compound of formula (I) in admixture or otherwise in association with one or more pharmaceutically acceptable carriers or excipients.
Another object of the present invention is to provide novel processes for the preparation of intermediates useful for the synthesis of fexofenadine and related compounds.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
Compounds of the formula (I) can be prepared using techniques and procedures well known and appreciated by one of ordinary skill in the art.
As used herein, straight or branched alkyl groups having from 1 to 6 carbon atoms as referred to herein are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, and straight- and branched-chain pentyl and hexyl.
The piperidine derivatives of the formula (I) can form pharmaceutically acceptable salts. Pharmaceutically acceptable acid addition salts of the compounds of this invention are those of any suitable inorganic or organic acid. Suitable inorganic acids are, for example, hydrochloric, hydrobromic, sulfuric, and phosphoric acids. Suitable organic acids include carboxylic acids, such as, acetic, propionic, glycolic, lactic, pyruvic, malonic, succinic, fumaric, malic, tartaric, citric, cyclamic, ascorbic, maleic, hydroxymaleic, and dihydroxymaleic, benzoic, phenylacetic, 4-aminobenzoic, 4-hydroxybenzoic, anthranillic, cinnamic, salicyclic, 4-aminosalicyclic, 2-phenoxybenzoic, 2-acetoxybenzoic, and mandelic acid, sulfonic acids, such as, methanesulfonic, ethanesulfonic and xcex2-hydroxyethanesulfonic acid. Non-toxic salts of the compounds of the above-identified formula formed with inorganic or organic bases are also included within the scope of this invention and include, for example, those of alkali metals, such as, sodium, potassium and lithium, alkaline earth metals, for example, calcium and magnesium, light metals of group IIIA, for example, aluminum, organic amines, such as, primary, secondary or tertiary amines, for example, cyclohexylamine, ethylamine, pyridine, methylaminoethanol and piperazine. The salts are prepared by conventional means, as for example, by treating a piperidine derivative of formula (I) with an appropriate acid or base.
The novel process for preparing the piperidine derivatives of formula (I) is set forth in Scheme A. in Scheme A, R1, and R2 are C1-C6alkyl wherein the C1-C6alkyl moiety is straight or branched; R3 is H or C1-C6alkyl wherein the C1-C6alkyl moiety is straight or branched; and X is Cl, Br or I. 
Scheme A provides a general synthetic procedure for preparing the compounds of formula (I).
In step A, a phenylacetyl halide (1) wherein X is Cl, Br, or I, is reacted with N-O-dimethylhydroxylamine hydrochloride to provide N-methoxy-N-methyl benzeneacetamide (2).
For example, a suitable phenylacetyl halide (1) is contacted with a molar excess of potassium carbonate in a suitable solvent such as toluene. Suitable phenylacetyl halides include phenylacetyl chloride, phenylacetyl bromide or phenylacetyl iodide. A preferred phenylacetyl halide is phenylacetyl chloride. A molar equivalent of N-O-dimethylhydroxylamine hydrochloride dissolved in water is then added. The reaction mixture is stirred for a period of time ranging from 1 to 24 hours at a temperature range of from 0xc2x0 C. to 60xc2x0 C. A preferred stirring time is 3 hours. A preferred temperature is 25xc2x0 C. N-methoxy-N-methyl-benzeneacetamide is (2) is recovered from the reaction zone by extractive methods as are known in the art.
In step B, N-methoxy-N-methyl-benzeneacetamide (2) is acylated with a suitable 4-halo-substituted butyrylhalide of the formula 
wherein each X is independently Cl, Br or I;
under Friedel-Crafts conditions to give a mixture of para, meta substituted xcfx89-halo-xcex1-keto-benzeneacetamide (3). Surprisingly, the para isomer is readily isolated by subsequent crystallization as set forth in step C.
For example, in step B, N-methoxy-N-methylbenzeneacetamide (2) is contacted with suitable 4-halo-substituted butyrylhalide under the general conditions of a Friedel-Crafts acylation using a suitable Lewis acid. Examples of suitable 4-halo-substituted butyrylhalides include 4-chlorobutyrylchloride, 4-bromobutyrylbromide, and the like. A preferred 4-halo-substituted butyrylhalide is 4 chlorobutyrylchloride. The reaction is carried out in a solvent, such as carbon disulfide, 1,2-dichloroethane, n-hexane, acetonitrile, 1-nitropropane, nitromethane, diethyl ether, carbon tetrachloride, methylene chloride, tetrachloroethane or nitrobenzene with dichloromethane being the preferred solvent. The reaction time varies from about xc2xd hour to 25 hours at a temperature range of from 0xc2x0 C. to 40xc2x0 C. A preferred stirring time is 6 hours. A preferred temperature is 40xc2x0 C. The mixture of para, meta substituted xcfx89-halo-xcex1-keto-benzeneacetamide (3) is recovered from the reaction zone by an aqueous quench followed by extractive methods as are known in the art.
Suitable Lewis acids for the acylation reaction described in step B are well known and appreciated in the art. Examples of suitable Lewis acids are boron trichloride, aluminum chloride, titanium tetrachloride, boron trifluoride, tin tetrachloride and zinc chloride. The selection and utilization of suitable Lewis acids for the acylation reaction of step B is well known and appreciated by one of ordinary skill in the art.
The para-substituted xcfx89-halo-xcex1-keto-benzeneacetamide (3) is purified by recrystallization techniques as set forth in step C.
For example, the product of the extractive methods as set forth in step B is stirred in a suitable organic solvent such as a mixture of heptane/ethyl acetate (ca. 4:1) and collected. The solid is dissolved in a suitable solvent such as ethyl acetate at a temperature range of from 25xc2x0 C. to 76xc2x0 C. A preferred temperature is 76xc2x0 C. The solution is then contacted with charcoal. This mixture is then filtered and diluted with a suitable solvent such as heptane. The resultant slurry is then heated until a homogenous solution is obtained. Substantially pure para-substituted xcfx89-halo-xcex1-keto-benzeneacetamide (4) crystallizes upon standing at room temperature.
In step D, the substantially pure para-substituted xcfx89-halo-xcex1-keto-benzeneacetamide (4) is hydrolyzed to give the 4-(cyclopropylcarbonyl)benzeneacetic acid (5).
For example, the substantially pure para-substituted xcfx89-halo-xcex1-keto-benzeneacetamide (4) is contacted with a molar excess of an appropriate base such as potassium hydroxide in a suitable solvent such as ethanol. The reactants are typically stirred together for a period of time ranging from 1 to 24 hours at a temperature range of from 0xc2x0 C. to 78xc2x0 C. A preferred stirring time is 18 hours. A preferred temperature is 25xc2x0 C. The 4-(cyclopropylcarbonyl)benzeneacetic acid (5) is recovered from the reaction zone by acidification and extractive methods as are known in the art.
In step E, the 4-(cyclopropylcarbonyl)benzeneacetic acid (5) is esterified to give the corresponding 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6).
For example, the appropriate 4-(cyclopropylcarbonyl)benzeneacetic acid (5) is reacted with an excess of an appropriate C1-C6 alcohol which is straight or branched in the presence of a catalytic amount of mineral acid, such as hydrochloric acid or sulfuric acid, hydrochloric acid being preferred, at a temperature range of from 25xc2x0 C. to 78xc2x0 C. The reactants are typically stirred together for a period of time ranging from 2 to 72 hours. A preferred stirring time is 24 hours. A preferred temperature is 25xc2x0 C. The corresponding 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6) is recovered from the reaction zone by basification and extractive methods as are known in the art. It can be purified by silica gel chromatography.
In step F, the appropriate 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6) is acylated with the appropriate acylating agent to give the corresponding [4(cyclopropylcarbonyl)phenyl]propanedioic acid diester (7).
For example, the appropriate 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6) is reacted with a slight molar excess of a suitable acylating agent. Suitable acylating agents include dialkylcarbonates, such as, dimethylcarbonate or diethylcarbonate; or chloroformates, such as, methyl chloroformate or ethyl chloroformate. The reaction is typically conducted in a suitable aprotic solvent in the presence of a suitable non-nucleophilic base from about 0.5 hour to 7 days and at a temperature of about 0xc2x0 C. to the reflux temperature of the solvent. A preferred stirring time is 3 days. A preferred temperature is 25xc2x0 C. Suitable solvents for the acylation reaction include tetrahydrofuran, dioxane, or tert-butyl methyl ether. A preferred solvent is tetrahydrofuran. Suitable non-nucleophilic bases for the acylation reaction include inorganic bases, for example, sodium bicarbonate, potassium bicarbonate, or hydrides, for example, sodium hydride or potassium hydride or alkoxides, for example, potassium tert-butoxide. A preferred base is sodium bis(trimethylsilyl)amide.
The derivative formed upon acylation is optionally alkylated with a suitable alkylating agent in situ subsequent to the acylation. Suitable alkylating agents include alkyl halides, such as, iodomethane, chloromethane or bromomethane; or dialkylsulfates, such as, dimethylsulfate or diethylsulfate. The reactants are typically stirred together for a period of time ranging from 1 to 48 hours at a temperature range of from 0xc2x0 C. to 30xc2x0 C. A preferred stirring time is 24 hours. A preferred temperature is 25xc2x0 C.
The corresponding [4-(cyclopropylcarbonyl)phenyl]propanedioic acid diester (7) is recovered from the reaction zone by extractive methods as are known in the art. It can be purified by silica gel chromatography and/or recrystallization.
While not necessary for utilization in the acylation and subsequent alkylation in step F, the keto functionality of the 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6) may be protected with a suitable protecting group. The selection and utilization of suitable protecting groups for the keto group of structure (6) is well known by one of ordinary skill in the art and is described in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d, Theodora W. Greene, Wiley (1981). For example, suitable protecting groups for the keto functionality include acyclic ketals such as dimethyl ketal; cyclic ketals such as 1,3-dioxanes and 1,3-dioxalanes; acyclic dithioketals such as S,S-dimethyl ketal; cyclic dithio ketals such as 1,3-dithiane and 1,3-dithiolane derivatives; acyclic monothio ketals; cyclic monothio ketals such as 1,3-oxathiolanes.
In step G, the appropriate [4-(cyclopropylcarbonyl)phenyl]propanedioic acid diester (7) is ring-opened to give the corresponding [4-(4-halo-1-oxobutyl)phenyl]propanedioic acid diester (8).
For example, the appropriate [4-(cyclopropylcarbonyl)phenyl]propanedioic acid diester (7) is contacted with a suitable hydrogen halide such as hydrogen chloride, hydrogen bromide, or hydrogen iodide in a suitable organic solvent or in the absence of solvent. Suitable organic solvents include alcohol solvents, such as, ethanol, methanol, isopropyl alcohol, or n-butanol; hydrocarbon solvents, such as, benzene, toluene or xylene; halogenated hydrocarbons, such as chlorobenzene, chloroform or methylene chloride or dimethylformamide or acetic acid or dioxane at a temperature range of from 0xc2x0 C. to 100xc2x0 C. The absence of solvent is preferred. The reactants are typically stirred together for a period of time ranging from 1 hour to 24 hours. A preferred stirring time is 4 hours to 16 hours. A preferred temperature range is 60xc2x0 C. to 80xc2x0 C. If solvent is present, the [4-(4-halo-1-oxo-butyl)phenyl]propanedioic acid diester (8) is recovered from the reaction zone by extractive methods as are known in the art and subsequent evaporation of the solvent.
In step H, the halo functionality of the appropriate [4-(4-halo-1-oxo-butyl)phenyl]propanedioic acid diester (8) is alkylated with xcex1-(4-pyridyl)benzhydrol (commercially available from Aldrich Chemicals) to give the corresponding [4-[4-[4-(hydroxydiphenylethyl)-1-piperidinyl]1-oxobutyl]phenyl]propanedioic acid diester (9).
For example, the alkylation reaction is carried out in a suitable solvent preferably in the presence of a non-nucleophilic base and optionally in the presence of a catalytic amount of an iodide source, such as potassium or sodium iodide. The reaction time varies from about 4 hours to 7 days and the reaction varies from about 25xc2x0 C. to the reflux temperature of the solvent. A preferred stirring time is 3 days. A preferred temperature is the reflux temperature of the solvent. Suitable solvent for the alkylation reaction include alcohol solvents such as, methanol, ethanol, isopropyl alcohol, or n-butanol; ketone solvents, such as, methyl isobutyl ketone; hydrocarbon solvents, such as, benzene, toluene or xylene, and mixtures thereof with water; halogenated hydrocarbons, such as, chlorobenzene or methylene chloride or dimethylformamide. A preferred solvent is toluene/water (10:4). Suitable non-nucleophilic bases for the alkylation reaction include inorganic bases, for example, sodium bicarbonate, potassium bicarbonate, or potassium carbonate or organic bases, such as, a trialkylamine, for example, triethylamine, or pyridine, or an excess of xcex1-(4-pyridyl)benzhydrol may be used. A preferred base is potassium carbonate.
The corresponding [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9) is recovered from the reaction zone by extractive methods as are known in the art. It can be purified by silica gel chromatography.
While not necessary for the utilization in the alkylation of step H, the keto functionality of the [(4-halo-1-oxo-butyl)phenyl]propanedioic acid diester (8) may be protected with a suitable protecting group. The selection and utilization of suitable protecting groups for the keto group of structure (8) is well known by one of ordinary skill in the art and is described in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d, Theodora W. Greene, Wiley (1981). For example, suitable protecting groups for the keto functionality include acyclic ketals such as dimethyl ketal; cyclic ketals such as 1,3-dioxanes and 1,3-dioxalanes; acyclic dithioketals such as S,S-dimethyl ketal; cyclic dithio ketals such as 1,3-dithiane and 1,3-dithiolane derivatives; acyclic monothio ketals; cyclic monothio ketals such as 1,3-oxathiolanes.
In step I, the appropriate [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9) is reduced selectively to the corresponding 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid ester (10). This is accomplished by utilizing a suitable selective reducing agent. A suitable selective reducing agent is a reagent or combination of reagents which will selectively reduce only one ester of the propanedioic acid diester functionality to the corresponding hydroxymethyl moiety while not reducing the second ester of the propanedioic acid diester functionality. Suitable selective reducing agents include lithium tri-tert-butoxyaluminohydride or the combination of a suitable silane and a suitable titanocene-based catalyst.
For example, the appropriate [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9) is contacted with a suitable selective reducing agent such as lithium tri-tert-butoxyaluminohydride in a suitable solvent such as tetrahydrofuran, diethyl ether, or dioxane. A preferred solvent is tetrahydrofuran. The reactants are typically stirred together for a period of time ranging from 0.5 hours to 168 hours at a temperature range of from 0xc2x0 C. to 65xc2x0 C. A preferred stirring time is 48 hours. A preferred temperature is 25xc2x0 C.
Catalytic reduction may also be employed in the preparation of 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid ester (10) from an appropriate [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9), using, for example, a suitable titanocene-based catalyst in which a suitable silane, such as, polymethylhydrosiloxane, serves as the stoichiometric reductant. Suitable titanocene-based catalysts include the active catalytic species commonly known as xe2x80x9cCp2TiHxe2x80x9d. It is well known by one of ordinary skill in the art that the active catalytic species xe2x80x9cCp2TiHxe2x80x9d may be generated, for example, by the addition of 2 equivalents of ethyl magnesium bromide to 1 equivalent of Cp2TiCl2 in a suitable solvent such as tetrahydrofuran.
For example, the catalytic reduction is carried out in a suitable solvent such as tetrahydrofuran or diethyl ether or dioxane at temperatures ranging from about 25xc2x0 C. to the reflux temperature of the solvent. A preferred temperature for use with the catalytic reduction is 65xc2x0 C. The reaction time varies from about 8 hours to 24 hours. A preferred stirring time is 18 hours. The 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid ester (10) is recovered from the reaction zone after work-up with Bu4NF and utilization of extractive methods as are known in the art. It can be purified by silica gel chromatography.
In addition, a chiral catalytic reduction may also be employed in the preparation of enantiomerically pure 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid ester (10) from an appropriate [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9), using an appropriate chiral titanocene system, such as, for example, is described in Journal of the American Chemical Society, 116, 11667-11670 (1994).
As one skilled in the art would appreciate, the [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9) wherein the keto group is protected must be reacted with an appropriate deprotecting reagent prior to the reduction reaction described in step I. The selection and utilization of appropriate deprotecting reagents is well known by one of ordinary skill in the art and is described in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d, Theodora W. Greene, Wiley (1981). For example, cleavage of a dimethylketal protecting group on the keto functionality of the [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]propanedioic acid diester (9) can be achieved by using iodotrimethylsilane or dilute acid as is known in the art.
In step J, the appropriate 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid ester (10) is optionally hydrolyzed to the corresponding 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid (11).
For example, hydrolysis may be achieved using methods known in the art such as potassium carbonate in methanol, methanolic ammonia, potassium carbonate, potassium hydroxide, calcium hydroxide, sodium hydroxide, magnesium hydroxide, sodium hydroxide/pyridine in methanol, potassium cyanide in ethanol and sodium hydroxide in aqueous alcohols, with sodium hydroxide being preferred. The reaction is typically carried out in an aqueous lower alcohol solvent, such as methanol, ethanol, isopropyl alcohol, n-butanol, 2-ethoxyethanol or ethylene glycol or pyridine. A preferred solvent is a mixture of tetrahydrofuran/methanol/water (3:2:1). The reaction is typically carried out at temperatures ranging from room temperature to the reflux temperature of the solvent. A preferred temperature is 65xc2x0 C. The reactants are typically stirred together for a period of time ranging from 1 to 24 hours. A preferred stirring time is 4 hours. The 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]-xcex1-(hydroxymethyl)-benzeneacetic acid (11) is recovered from the reaction zone by acidification and extractive methods as are known in the art.
Of course it is understood that the compound of formula (I) may exist in a variety of stereoisomers. The compound has more than one chiral center. For example, the benzylic carbon to which the carboxyl, hydroxymethyl and methyl groups attach may exist in the (R) or the (S) form. In addition, the benzylic carbon to which the hydroxy, hydrogen and alkyl amino groups attach may exist in the (R) or the (S) form. It is further understood that the present invention encompasses those compounds of formula (I) in each of their various structural and stereo isomeric configurations as individual isomers and as mixtures of isomers.
An alternative novel process for the preparation of 4-(cyclopropylcarbonyl)benzeneacetic acid is set forth in Scheme B. This compound is useful for the synthesis of compounds of formula (I) as well as fexofenadine and related compounds. In Scheme B, R1 is C1-C6alkyl and the C1-C6alkyl moiety is straight or branched. 
In step a of Scheme B, the appropriate benzeneacetic acid ester (1) wherein R1 is C1-C6alkyl and the C1-C6alkyl moiety is straight or branched, is acylated with a suitable 4-halo-substituted butyrylhalide of the formula 
wherein each X is independently Cl, Br, or I, under Friedel-Crafts conditions to give a mixture of the corresponding para, meta substituted xcfx89-halo-xcex1-keto-benzeneacetic acid ester (2) wherein X is Cl, Br, or I.
For example, in step a, the appropriate benzeneacetic acid ester (1) is contacted with a 4-halo-substituted butyrylhalide under the general conditions of a Friedel-Crafts acylation using a suitable Lewis acid. Examples of suitable 4-halo-substituted butyrylhalides include 4-chlorobutyrylchloride, 4-bromobutyrylbromide, and the like. A preferred 4-halo-substituted butyrylhalide is 4-chlorobutyrylchloride. The reaction is carried out in a solvent, such as carbon disulfide, 1,2-dichloroethane, n-hexane, acetonitrile, 1-nitropropane, nitromethane, diethyl ether, carbon tetrachloride, methylene chloride, tetrachloroethane or nitrobenzene with dichloromethane being the preferred solvent. The reaction time varies from about xc2xd hour to 25 hours at a temperature range of from 0xc2x0 C. to 40xc2x0 C. A preferred stirring time is 6 hours. A preferred temperature is 40xc2x0 C. The mixture of para, meta substituted xcfx89-halo-xcex1-keto-benzeneacetic acid ester (2) is recovered from the reaction zone by an aqueous quench followed by extractive methods as are known in the art.
Suitable Lewis acids for the acylation reaction described in step a are well known and appreciated in the art. Examples of suitable Lewis acids are boron trichloride, aluminum chloride, titanium tetrachloride, boron trifluoride, tin tetrachloride and zinc chloride. The selection and utilization of suitable Lewis acids for the acylation reaction of step a is well known and appreciated by one of ordinary skill in the art.
In step b of Scheme B, the mixture of meta- and para-substituted xcfx89-halo-xcex1-keto-benzeneacetic acid ester (2) is hydrolyzed to give a mixture of meta- and para-substituted (cyclopropylcarbonyl)benzeneacetic acid (3).
For example, the mixture of meta- and para-substituted xcfx89-halo-xcex1-keto-benzeneacetic acid (2) is contacted with a molar excess of an appropriate base such as lithium hydroxide or potassium hydroxide in a suitable solvent such as ethanol. The reactants are typically stirred together for a period of time ranging from 1 to 24 hours at a temperature range of from 0xc2x0 C. to 78xc2x0 C. A preferred stirring time is 18 hours. A preferred temperature is 25xc2x0 C. The meta- and para-substituted (cyclopropylcarbonyl)benzeneacetic acid (3) is recovered from the reaction zone by acidification and extractive methods as are known in the art.
Surprisingly, the substantially pure para isomer is readily isolated by subsequent crystallization as set forth in step c of Scheme B.
For example, the product of the extractive methods as set forth in step b is dissolved in a suitable organic solvent such as a mixture of heptane/ethyl acetate (ca. 4:1) with heating to reflux. The solution is treated with charcoal and filtered. Upon cooling, the resultant solid is collected and recrystallized from a suitable organic solvent such as ethyl acetate/heptane. Substantially pure para-substituted (cyclopropylcarbonyl)benzeneacetic acid (4) crystallizes upon standing at room temperature.
As shown previously herein, 4-(cyclopropylcarbonyl)benzeneacetic acid has utility as an intermediate in the synthesis of compounds of formula (I). 4-(Cyclopropylcarbonyl)benzeneacetic acid may also be used as an intermediate in the process of preparing compounds of formula (7) as shown in Scheme C. Compounds of formula (7) include fexofenadine and related compounds. 
In step a of Scheme C, the 4-(cyclopropylcarbonyl)benzeneacetic acid (1) is esterified to give the corresponding 4-(cyclopropylcarbonyl)benzeneacetic acid ester (2) wherein R1 is C1-C6alkyl and the C1-C6alkyl moiety is straight or branched, under conditions as set forth in Scheme A, Step E.
In step b of Scheme C, the 4-(cyclopropylcarbonyl)benzeneacetic acid ester (2) is alkylated with a suitable alkylating agent to provide a corresponding alkylated [4-(cyclopropylcarbonyl)phenyl]benzeneacetic acid ester (3) wherein R1 is as previously defined in step a and R2 and R3 are each independently C1-C6alkyl wherein the C1-C6alkyl moiety is straight or branched.
For example, the reaction is typically conducted in a suitable aprotic solvent in the presence of a suitable non-nucleophilic base. Suitable solvents for the alkylation reaction include diglyme, tetrahydrofuran, dioxane, or tert-butyl methyl ether. A preferred solvent is diglyme. Suitable non-nucleophilic bases for the alkylation reaction include sodium bis(trimethylsilyl)amide, inorganic bases, for example, sodium bicarbonate, potassium bicarbonate, or hydrides, for example, sodium hydride or potassium hydride or alkoxides, for example, potassium tert-butoxide. A preferred base is potassium tert-butoxide. Suitable alkylating agents include alkyl halides, such as, iodomethane, chloromethane or bromomethane; or dialkylsulfates, such as, dimethylsulfate, or diethylsulfate. The reactants are typically stirred together for a period of time ranging from 1 to 48 hours at a temperature range of from 0xc2x0 C. to 80xc2x0 C.
In step c of Scheme C, the appropriate alkylated [4-(cyclopropylcarbonyl)phenyl]benzeneacetic acid ester (3) is ring opened to provide the corresponding [4-(4-halo-1-oxo-butyl)phenyl] benzene acetic acid ester (4) wherein R1, R2 and R3 are as previously defined in step b and X is Cl, Br or I. The reaction occurs under conditions set forth in step G of Scheme A.
In step d, the appropriate [4-(4-halo-1-oxo-butyl)phenyl] benzene acetic acid ester (4) is alkylated with xcex1-(4-pyridyl)benzhydrol to produce a [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxo-butyl]phenyl]benzeneacetic acid ester (5) wherein R1, R2 and R3 are as previously defined in step b, under conditions that were previously disclosed in U.S. Pat. No. 4,254,129, the disclosure of which is herein incorporated by reference.
In step e of Scheme C, the appropriate [4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-oxobutyl]phenyl]benzeneacetic acid ester (5) is reacted with a suitable reducing agent to produce a 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]benzeneacetic acid ester (6) wherein R1, R2 and R3 are as previously defined in step b, under conditions that were previously disclosed in U.S. Pat. No. 4,254,129. Suitable reducing agents include, for example, sodium borohydride or potassium borohydride. Catalytic reduction using, for example, Raney nickel, palladium, platinum, or rhodium catalysts, may also be employed in step e of Scheme C.
In step f of Scheme C, the 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]benzeneacetic acid ester (6) is optionally hydrolyzed to produce the 4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]benzeneacetic acid (7) wherein R2 and R3 are as previously defined in step b, under conditions that were previously disclosed in U.S. Pat. No. 4,254,129.
While not necessary for utilization in alkylation steps b and d, the keto functionality of the 4-(cyclopropylcarbonyl)benzeneacetic acid ester (6) may be protected with a suitable protecting group. The selection and utilization of suitable protecting groups for the keto group of structure (6) is well known by one of ordinary skill in the art and is described in xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d, Theodora W. Greene, Wiley (1981). For example, suitable protecting groups for the keto functionality include acyclic ketals such as dimethyl ketal; cyclic ketals such as 1,3-dioxanes and 1,3-dioxalanes; acyclic dithioketals such as S,S-dimethyl ketal; cyclic dithio ketals such as 1,3-dithiane and 1,3-dithiolane derivatives; acyclic monothio ketals; cyclic monothio ketals such as 1,3-oxathiolanes.
The following examples present typical syntheses as described in Schemes A B and C. Starting materials for use in Schemes A, B and C are readily available to one of ordinary skill in the art. These examples are understood to be illustrative only and are not intended to limit the scope of the present invention in any way. As used herein (throughout the specification), the following terms have the indicated meanings: xe2x80x9cgxe2x80x9d refers to grams; xe2x80x9cmmolxe2x80x9d refers to millimoles; xe2x80x9cmL refers to milliliters; xe2x80x9cbpxe2x80x9d refers to boiling point; xe2x80x9cmpxe2x80x9d refers to melting point; xe2x80x9cxc2x0C.xe2x80x9d refers to degrees Celsius; xe2x80x9cmm Hgxe2x80x9d refers to millimeters of mercury; xe2x80x9cxcexcLxe2x80x9d refers to microliters; xe2x80x9cxcexcgxe2x80x9d refers to micrograms; and xe2x80x9cxcexcMxe2x80x9d refers to micromolar.